Resonant pulsing circuit



byjproviding the lamps with greater dead spaces.

United States Pat m.b.H.

Filed Oct. 7, 1959, Ser. No. 844,890 Claims priority, application Germany, Oct. 9, 1958 6 Claims. (Cl. 315-183) This invention relates to a circuit for impulse operation of electric discharge lamps or flashtubes.

In German Auslegeschrift No. 1,044,443 there is disclosed a color matching device which permits colormatching in a daylike illumination at a color temperature of about 5000 to 7000 K. and in which an electric discharge lamp or fl-ashtube is used as the light source. This lamp is intended particularly for DC. operation with a condenser voltage of less than 500 volts. It has a filling of rare gas, preferably xenon, at one atmosphere pressure or less, and is operated periodically with current impulses of high momentary intensity. The lamp is operated in such a manner that pulsating DC. voltage supplied by a rectifier is applied across a charging resistance to the operating condenser and to the lamp.

The object of the present invention is to provide an improved circuit for impulse operation of such lamps or fiashtubes.

In the operating circuit according to the present invention, there is used a resonance connection in which a pub sating DC. voltage across an inductance and a capacity is applied to the flashtube or lamp. An electron control device such as a thyratron may be used to trigger or fire the flashtube at the resonant frequency. The maximum value of the condenser voltage is not obtained when the circuit is first switched on but occurs after a short delay. This arrangement has the advantage that at the initially low cold pressure of the lamp at which the starting and operating voltages are lower than at the increased pressure during sustained operation, any breakdown in the lamp is prevented. By amplifying the voltage in the resonance circuit, the voltage applied to the lamp adapts to the operating voltage which increases with increasing pressure. The frequency of the resonance circuit should amount to at least 50 cycles per second in order to prevent any flickering effect.

' Because the lamp voltage is increased by the resonance, a smaller operating condenser sufiices for equal lamp wattage. However when using a smaller capacity the discharge takcs place across the gas path in shorter time and has higher peaks in output. This would cause a change in color temperature of the discharge. To keep the color temperature at a desired value, the duration of the discharge may, according to the present invention, be extended by connecting a damping choke between the flashtube or lamp and the resonance circuit. The value of the inductance is, suitably, chosen in such a manner that the aperiodic limiting case for the discharge is achieved. At the same time the use of a damping choke reduces the temporary steep current increase which tends to be in- V jurious. to. the cathodes.

All periodically operated impulse lamps have, in prinl ciple, a narrow limited range of operating voltage which increases on connection of the lamp because of the higher pressure in the operating condition. Shifting of the operating range toward'higher voltages may be decreased Manufacture of such lamps is, however, more difficult and more expensive because of their special form.

. Animpontant'advantage of the circuit according to the present invention consists in that it admits of the use of ice lamps without dead space because of the adaptation of the voltage on the condenser to the operating voltage which varies in consequence of the increasing pressure during operation. This permits a considerable simplifi cation and reduction in price of the device. Another ad vantage consists in that with lamps having no dead space,- the damping choke brings about a higher light output.

The lamps preferably may have an elongated shape and are operated in conjunction with a starting device suitable for obtaining a silent spark discharge over long time durations. Such a starting device may comprise a sheet strip resiliently pressed from outside against the lamp envelope in parallel with the discharge path.

Another advantage of the present circuit consists in that the chokes have practically no such losses as occur with the more generally used charging resistances.

For further objects and advantages, attention is now directed to the following detailed description of a pre ferred embodiment taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a schematic diagram of a circuit for impulse operation embodying the invention;

FIG. 2 illustrates a suitable discharge lamp or flashtube; and

FIG. 3 is a curve showing certain operating characteristics of the circuit of FIG. 1.

Referring to FIG. 1, the pulsing circuit may be energized from 220 volt, 60 cycle A.C. supply lines at terminals 1, 2 through switch 3 and resistor fuse 4. The operating constants and values of circuit elements stated herein are given by way of example only. The pulsating DC. voltage supplied by bridge rectifier 5 is applied across a choke 6 of about 0.3 henry to operating condenser 7 of about 10 microfarads and to the impulse daylight lamp or fiashtube 8. Choke 6 and condenser 7 form a circuit which is series resonant at about the frequency of the pulsating DC. voltage or full wave rectified waveform supplied by bridge rectifier 5, the fundamental frequency thereof being twice the A.C. supply frequency. A damping choke 9 of about microhenrys is connected between the resonant circuit and the lamp.

The breakdown voltage of the lamp, even at the relatively low filling pressure, is above approximately 300 volts so that condenser 7 cannot discharge through the lamp. The breakdown of the lamp is caused by a high frequency starting impulse. This starting impulse is produced by discharging a condenser 10 of 0.1 microfarad through the primary winding 11 of a pulse transformer 12 and the moment of discharge is determined by a thyratron or gas discharge tube 13. The pulsating DC. voltage developed across condenser 7 of the resonant circuit is applied to the anode of the thyratron through contacts 14 of a relay 15, manual switch 16, and load resistance 17. A pulsating negative voltage of a few volts is developed across resistor 18 as a result of rectification by diodes 19 and 20 of the voltage produced by secondary winding 21 of transformer 22 whose primary wind ing 23 is energized from the A.C. supply. This voltage is applied'through'current limiting resistor 24 to the grid or control electrode of thyratron '13. Thus the signal applied to the control grid of the thyratron is of the same frequency as that applied to the anode but is shifted in phase Firing of the thyratron takes place a short time before the A.C. voltage in the resonant circuit passes through zero. The discharge current through the primary of pulse transformer 12 produces a high voltage pulse (v.g. 6 kv.) in its secondary winding 25 which is applied to'the starting strip 26 of lamp or flashtube 8.

. During operation, the pressure in the lamp about doutales: and thevoltage applied to the lamp rises in conselamp at each impulse.

'such as a silicon controlled rectifier.

the voltage across resonance condenser 7 and also at the anode of thyratron 13 as a functionv of time. Dotted line curve 28 illustrates the biasing voltage applied at the grid or control electrode of the thyratron as a function of time. With a 60 cycle A.C. supply voltage, charging and discharging of the condenser is repeated every 1 second and the impulse frequency ofthe lamp is 120 cycles per second. In consequence of the resonance effect, the amplitude of the voltage across condenser 7 and which is applied to lamp 8 increases about 1.5 times to the full resonance level after a few half waves. The purpose of relay i is to provide a delay of about 30 seconds between the enengization of the circuit and the application of anode voltage to thyratron tube 13 in order to allow preheat of the cathode by winding 29 of transformer 22. Resistor 3t} and capacitor 31 prevent chattering of the relay.

FIG. 2 shows a daylight impulse lamp 32 without dead space suitable for use in the present circuit and capable of a power input of about 100 watts. The lamp has an elongated shape and is about 12 centimeters long (dimension L and is provided with tubular end caps or bases 33. The capillary tube within the lamp in which the discharge takes place has an inner diameter of 'about 2 mm. and a length measured between the tips of electrodes 34 (dimension L of about 8 centimeters. Filling pressure on account of the great inter-electrode distance and low operating voltage is below 1 atmosphere. Relatively long discharge durations and low operating voltages result in relatively low peak currents of 'about 40 amperes. This spares the lamp and permits a lamp life of about 500 hours which is close to that of stationary operated, that is non-impulse operated, lamps. The lamps may be operated beyond this time, however variations in color may occur. Lamp efficiency amounts to about 13 lumens per watt so that for an elongated area of 50 x 50 cm. with a luminaire eificiency of 30 an illumination of about 1600 lux is obtained.

A discharge lamp or flashtube impulse operated as described herein has a continuum in its radiation spectrum which is quite similar to that of a stationary operated (that is non-impulsed operated) xenon lamp. If it is desired to eliminate or reduce flickering as much as possible for certain purposes, lamps as disclosed in the present invention may also be operated in three-phase connection.

It will be understood that the specific circuit which has been described herein is intended as exemplary and not as limitative of the invention. Obviously a semi-conductive control device may be used in lieu of the thyratron which has been described for triggering the flashtube or Such semi-conductive control device may, with appropriate circuit modifications, take the form of a transistor or that of a controlled rectifier The appended claims are therefore intended to cover any such modifications coming within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters 'Patent of the United States is:

1. An impulse operating circuit for a discharge lamp comprising an alternating current source of predetermined frequency, a rectifier circuit connected across said source and producing a full wave rectified wayeform output having a fundamental frequency twice said predetermined frequency, a circuit comprising an inductance and a capacitance connected in series across said rectifier cir- 4 tified waveform, said discharge lamp being connected across said capacitance, and means for supplying high voltage pulses to said discharge lamp to trigger it at an impulse frequency corresponding to the fundamental frequency of said full wave rectified Waveform.

2. An impulse operating circuit for an electric discharge lamp containing an inert rare gas. filling comprising an alternating current. source of predetermined frequency, a rectifier circuit connected across said source and producing a full wave rectified waveform output having a fundamental frequency twice said predetermined frequency, a resonance circuit comprising an inductance and a capacitance connected in series across said rectifier circuit and which are series resonant at approximately the fundamental frequency of said full wave rectified waveform, said discharge lamp being connected across said capacitance, said resonance circuit being proportioned relative to said lamp such that the voltage ap plied to the lamp increases from an initial value at starting to a higher value during normal operation, and means for supplying high voltage pulses to said discharge lamp to trigger it at an impulse frequency corresponding to the fundamental frequency of said full wave rectified waveform.

3. An impulse operating circuit for an electric discharge lamp containing an inert rare gas filling'cornprising an alternating current source of predetermined frequency, a rectifier circuit connected across said source and producing a full wave rectified waveform output having a fundamental frequency twice said predetermined frequency, a resonance circuit comprising an inductance and a capacitance connected in series across .said rectifier circuit and which are series resonant at approximately the fundamental frequency of said full wave rectified waveform, said discharge lamp being connected across said capacitance, said resonance circuit being proportioned relative to said lamp such that the voltage applied to the lamp increases from an initial value at starting .to a higher value during normal operation, and a triggering circuit comprising an electron control device energized by the voltage developed across said capacitance and supplying pulses to said discharge lamp, and means for firing said electron control device at an impulse frequency corresponding to the fundamental frequency, of said full wave rectified waveform.

4. A circuit as defined in claim 3 including a damping choke connected in series with said discharge lamp across said capacitance for increasing the duration of the discharge at each impulse.

5. An impulse operating circuit for an electric 'discharge lamp containing an inert rare gas filling comprising an alternating current source of predetermined frequency, a rectifier circuit connected across said source and producing a full wave rectified waveform output having a fundamental frequency twice said predetermined frequency, a resonance circuit comprising an inductance and a capacitance connected in series across said rectifier circuit and which are series resonant at approximately the fundamental frequency of said full wave rectified waveform, said discharge lamp being vconnected across said capacitance, said resonance circuit being proportioned relative to said lamp such thatthe voltage applied to the lamp increases from an initial value at starting to a higher value during normaloperation, and a triggering circuit comprising an electron control device energized by the voltagedeveloped across said capacitance, means for firing'said electron control device at an impulse frequency corresponding to the fundamental frequency of said full wave rectifiedwaveform, and a-pulse transformer energized by said' electron control device and supplying high voltage pulses to said discharge lamp to trigger it at the impulse frequency. '1 V r n 6. An impulse operating circuit for an electr c, discharge lamp containing an inert rare gas fillingat a pressure not over one atmosphere comprising an alternating current source of predetermined frequency, a rectifier circuit connected across said source and producing a full wave rectified waveform output having a fundamental frequency twice said predetermined frequency, a resonance circuit comprising an inductance and a capacitance connected in series across said rectifier circuit and which are series resonant at approximately the fundamental frequency of said full wave rectified waveform, said discharge lamp being connected across said capacitance, said resonance circuit being proportioned relative to said lamp such that the voltage applied to the lamp increases from an initial value at starting to a value about 1.5 times higher during normal operation while the filling pressure in said lamp about doubles, and a triggering circuit comprising a thyratron energized by the voltage developed across said capacitance, means for supplying a signal to the control electrode of said thyartron to fire it at an impulse frequency corresponding to the fundamental frequency of said full wave rectified waveform, and a pulse transformer energized by said thyratron and supplying high voltage pulses to said discharge lamp to trigger it at the impulse frequency.

References Cited in the file of this patent UNITED STATES PATENTS 

